Uranium photo-electric ttjbe



July 21, 1931. H. c. RENTSCHLER ET AL 1,815,073

URANIUM PHOTO ELECTRIC TUBE Filed June 12, 1929 24170 zabo 32 00 WAVE LENGTH m ANqsTRo/w UN/TJ INVENTOR H. ORE SCHLER ATTORNEY entrance of air into the envelope after the formation of the cathode, since exposure of the uranium cathode to the atmosphere, even for short periods, may impair its sensitivity.

In Fig. 2 we have'shown the relation between the wave length of the incident light and the'current output of a tube employing an envelope which absorbs the ultra-violet light of very short Wave length especially those below approximately 2400 Angstrom units, so as to render the tube sensitive only to a restricted band of frequencies in the region most desirable for erythema treatments. These curves are approximate only. Curve 31 designates approximately the relation of the per cent transmission 0 the ultraviolet radiations through the wall of the envelope, curve 32 the total current or photoelectric sensitivity of the uranium cathode, assuming no absorption of radiations in the envelope, and curve 33 is a resultant curve indicating the efiect of the energy absorption of the glass (curve 31) on the current output (curve 32) of, the cathode. The form of the curve 31 will vary somewhat with different glass compositions and may be modified by H employing glass of different thicknesses, so that the elfect of the absorption of the ultra violet radiations in the glass on the output of the tube, may be modified.

With the form of curves shown, the maximum sensitivit occurs at about 2900 Augstrom units which is in the narrow region of the spectrum most suitable for erythema treatment.

The current output of the tube falls off quite rapidly each side of the peak so that the tube is not appreciably sensitive exce t to a veiiy narrow band of ultra violet radiations.

he ak of the curve 33 may be shifted to the ower wave length re ion by employin a thinner envelope or y employing a thin window in the envelope so as to decrease the absorption of the lower wave len -h radiations or it ma be shifted to the igher wave length region by employing a glass less transparent to ultra violet. I q

We are aware that the invention may be embodied in a variety of s ecific forms without departing from the s 1rit or essential attributes thereof and we esire that the present embodiment be considered in all respects as illustrative and not restricted, reference anode and a cathode therein, said cathode comprising a film of uranium metal on the wall of the envelope.

3. A photo electric tube comprising an envelo transparent to ultra-violet hght, an ano e and a cathode therein, said cathode comprising a layer of a noble metal having deposited thereon a quantity of uranium.

4. A photo electric tube comprising an envelope transparent to ultra-violet light, an anode and a cathode therein, said cathode comprising a coating of gold on the envelope having a lm of uranium thereon.

5. An electron discharge device comprising an enclosing envelope, an anode and a photo sensitive cathode, said cathode bein comprised substantially of uranium and sai envelope having a section thereof comprised of glass permeable to radiation of wave lengths less than about 45 Angstroms.

6. An electron discharge device comprising an envelope permeable to radiation approximating 2900 Angstroms, an anode and a photo sensitive cathode, said cathode being comprised 'of uranium.

7. A photo electric tube comprising an envelope transparent to ultra-violet. hght, an anode and a cathode therein, said cathode consistin of metallic uranium.

8. A photo electric tube comprising an envelope having at least a portion transparent to u tra-violet light, an anode and a cathode therein, said cathode being composed of uranium and said envelope being substantially opaque to radiations havin a wave length below approximately 2400 ingstrom units.

9. A photo electric tube comprisin an envelope having an anode and a catho e therein, said cathode being com osed of uranium and at least a part of sai envelo e, being transparent to ultra-violet light 0 a wave length above approximately 2400 Angstrom units but havin a low per cent transmission of radiations o a wave length shorter than about 2400 Angstrom units.

In testimony whereof, we have hereunto subscribed our names this 8th day of June HARVEY C. RENTSCHLER. DONALD E. HEN RY.

being had to the appended claims rather than the foregoing description to indicate the scope of the invention.

What is claimed is:

1. An electron discharge device comprising an envelop: transparent to radiation of wave lengths tween about 2400 Angstroms and about 4500 Angstroms, an anode and a photo sensitive cathode, said cathode be'ing comprised of uranium.

2. A photo electric tube comprising an envelope transparent to ultra-violet hght, an

Patented July 21, 1931 UNITED STATES PATENT OFFICE HARVEY C. RENTSCHLER, OF EAST ORANGE, AND DONALD E. HENRY, OF BLOOMFIEIID, NEW JERSEY, ASSIGNORS TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA URANIUM PHOTO-ELECTRIC TUBE Application filed June 12,

This invention relates to a photo-electric tube and more particularly to a tube which is sensitive only in the ultra violet region of the spectrum.

In a copending application Serial No. 360,667, filed May 6, 1929 in the name of H. C. Rentschler, the-re is described and claimed a photo electric tube in which the sensitivity starts in the blue region of the spectrum and extends into the ultra violet region. This restricted sensitivity is obtained by employing as the cathode of the tube ametal of the cerium group of rare earth metals, and more particularly misch metal, which is a mixture of such metals.

In another copending application of H. C. Rentschler, Serial No. 360,666, filed May 6, 1929 there is described a photo-electric tube in which the sensitivity is restricted entirely to the ultra violet region starting with radiations having a wave lengthof about-3600- Angstrom units. This restricted sensitivity is obtained by employing thorium for the. cathode. This latter photo-electric tube is particularly useful for measuringultra violet light employed for erythema treatment. For such .treatment the range of useful rays is restricted to a narrow band each side of about 2900 Angstrom units, and when a thorium cathode isemployed for'the tube, in an en-' velope which is opaque to waves of extremely short Wave length, a tube may be produced which has a maximum sensitivity atabout 2900 Angstrom units and only a low order of sensitivity at wavelengths appreciably above and below this value.

One of the objects of the present invention is to produce a photo electric tube in which the sensitivity oes not start except in response to still lower wave lengths than the thorium cathode photo electric tube.

Another object is to provide a photo-electrio tube which is sensitiveonly to a very narrow band of radiations having a maximum sensitivity of about 2900 Angstrom units.

A still further object is to produce a photoelectric tube which is substantially non-sensitive to radiations above about 3200 Angstrom units.

A further object is to provide an improved 1929. Serial No. 370,223.

method of producing a photosensitive electrode.

Other objects and advantages will hereinafter appear.

I have discovered that the metal uranium when thoroughly cleaned and treated in accordance with a definite schedule exhibits a normal photo-electric effect which starts at about 3300 Angstrom units, but which does not produce a measurable current above about 3200 Angstrom units. 1

The photosensitivity of the uranium cathode is in suchregion that it is entirely nonsensitive to light filtered through ordinary window glass.

By employing the uranium cathode in an envelope composed of a glass which is opaque to radiations of short wave length and es pecially those below 2400 Angstrom units, such as Gorex glass, the .band of the ultra violet region to which the-tube is sensitive may be mademorenarrow than in the case of the thorium photo-electricitube, and the sensitivity of the cell thereby z estricted more close- 1y to the particular band' of radiations which are efi'ective in erythema treatment. I

In producing a photo-electric tube in accordance with our inventionwe may employ uranium for both the anode and the cathode, although it is to be understood that the anode may be composed of another metal such as nickel. The cathode may consist of a sheet of uranium but preferably is formed as a thin deposit of uranium on the wall of the en- 'velope in contact with the leading-in conductor.

In order to render the uranium cathode active 1t is necessary to thoroughly clean the surface of all impurities, oxides, etc. This a uranium anode and produce the coating on the wall by sputtering the uranium from the 

